Cartridge within-a-cavity valves are widely used for controlling many fluids, including applications where the flow control of high pressure hydraulic fluid is desired. Cartridge-type valves are widely used because the internal components of the valve may be easily removed and replaced from a manifold cavity for maintenance and repair.
Cartridge valves are commonly used in a manifold cavity of the type shown in FIG. 1. Referring to this figure, fluid enters the cavity through port 6 and exhausts through port 5. A cylinder 4 receives the valve at the base of the manifold. At least two types of prior art valves have been employed in this application and these are depicted in FIGS. 2 and 3. In both cases, a threaded stem is turned by a handle (as shown in FIG. 1) which moves a tapered piston into and out of contact with the valve seat. As seen in both of these illustrations, each design requires at least three parts; a gland (a), a stem (b), and a valve seat module (c) which threads into the bottom of the gland. The valve seat module includes ports 1 and 2 which receive and exhaust all fluid that moves through the valve.
A significant problem with these prior art valves is leakage. Leakage often occurs because both the stem and the valve seat module are manufactured with threads in the right-hand helix. Upon installation of the valve assembly, the threaded joint between the valve seat module and the gland is secured by a liquid-locking compound. This joint is labeled feature "d" on FIGS. 2 and 3. In use, it is possible to break free this secured threaded connection when turning the valve handle in the clockwise direction to close the valve. This occurs because rotation of the stem against the valve seat imparts a torque to the valve seat module which loosens it. When the threaded engagement between the stem and the valve seat module breaks free, both move in the same direction preventing further force being applied to the stem sealing area. This results in unwanted leakage past the valve seal.
Prior art valves are also deficient in that they do not conform with the desired industry practice of providing sealing valves with "single-line contact". Single-line contact means that each mating component must be concentric so that the contact between them is a continuous line. If this condition is not met, then parts are said to be "eccentric" and the contact patch between mating parts is only a single point. This results in leakage past the other areas along the theoretical contact line that are not touching. Without a consistent single center line throughout the valve and no other means of providing a justified seating service once the valve is assembled, single-line contact sealing of the valve cannot occur.
A further problem with both of these prior art valves is valve seat wear. In high pressure applications, the valve stem is required to be tightly screwed down against the valve seat which has very limited surface area. Hence, the parts wear quickly and need to be replaced often. Also, neither design provides the desired efficiency or sensitive flow metering due to fluid turbulence in the area of the valve seat.
The closest patent prior art which the applicant is aware is U.S. Pat. No. 3,654,950, issued to John R. Hamm, Apr. 11, 1972. The device described in this reference is pertinent in that it shows a reciprocating sleeve-type valve, but it fails to teach or suggest the novel claimed features of the present invention.